Hello Aza,

Aza D. Oberman wrote:
> . . . . . . .   We spent quite a bit of time before
> figuring out that the NS1645 UART on the original IBM serial and
> serial/parallel port adapter card was wired in such a way that one could not
> use software to turn off all the handshaking requirements for reading
> RS-232.  It *had* to "see" a device out there before it would receive
> anything.

As far as I know the IBM-PC and later the PC-XT were standard delivered 
with a monochrome display/printer adapter. An 'Asynchronous 
Communications Adapter' was an option.  This adapter was equiped with an 
NS8250 and a 25-pin subD connector (IBM Tech Ref April 1984).

The combined asyn/printer adapter came with the PC/AT, and this adapter 
was equiped with an NS16450 and a 9-pin subD connector (IBM Tech Ref for 
the PC/AT, September 1985). This is probably the one you are referring 
to?  I have still such an adapter in use on an old Pentium I use for 
experiments. Maybe it is a later version, but I have never experienced 
problems with flow control lines.


> Three wire (RX, TX, & Common) RS-232 is certainly convenient, but I still
> question if it is a good practice to not at least strap the handshaking
> lines when designing a RS-232 device. 

I agree. When I build a PIC-based device with UART I either implement 
CTS/RTS handshaking or use loop-backs with a current limiting resistor.

[Ironically, I believe the "RS" in
> "RS-232" stands for "Recommended Standard" -- makes one wonder what the
> official one  is...]

Isn't it an EIA or IEEE standard today?

Regards, Rob.

-- 
Rob Hamerling, Vianen, NL phone +31-347-322822
homepage: http://www.robh.nl/
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